Evaluation of Multilayer Silicon Carbide Composite Cladding Under Loss of Coolant Accident ...

164 Pages·2015·9.88 MB·English

Evaluation of Multilayer Silicon Carbide Composite Cladding
Under Loss of Coolant Accident Conditions

By

Gregory Welch Daines
B.S. Mechanical Engineering (2014)
The University of Maryland at College Park

SUBMITTED TO THE DEPARTMENT OF NUCLEAR SCIENCE AND ENGINEERING IN PARTIAL
FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF

MASTER OF SCIENCE IN NUCLEAR SCIENCE AND ENGINEERING
AT THE
MASSACHUSETTS INSTITUTE OF TECHNOLOGY

February 2016

© 2016 Massachusetts Institute of Technology. All rights reserved.

Signature of Author: ____________________________________________________________________
Gregory Welch Daines
Department of Nuclear Science and Engineering
December 17, 2015

Certified by: __________________________________________________________________________
Michael P. Short, Ph.D.
Assistant Professor of Nuclear Science and Engineering
Thesis Supervisor

Certified by: __________________________________________________________________________
Thomas J. McKrell, Ph.D.
Research Scientist
Thesis Reader

Accepted by: __________________________________________________________________________
Ju Li, Ph.D.
Battelle Energy Alliance Professor of Nuclear Science and Engineering
And Professor of Materials Science and Engineering
Chairman, Department Committee on Graduate Students
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Evaluation of Multilayer Silicon Carbide Composite Cladding
Under Loss of Coolant Accident Conditions

by

Gregory Welch Daines

Submitted to the Department of Nuclear Science and Engineering
on December 17, 2015 in Partial Fulfillment of the
Requirements for the Degree of Master of Science
Abstract
Silicon carbide (SiC) has been proposed as an alternative to zirconium alloys used in current light water
reactor (LWR) fuel cladding because it exhibits superior corrosion characteristics, high-temperature
strength, and a 1000˚C higher melting temperature, all of which are important during a loss of coolant
accident (LOCA). To improve the performance of SiC cladding, a multilayered architecture consisting of
layers of monolithic SiC (mSiC) and SiC/SiC ceramic matrix composite (CMC) has been proposed.

In this work, the mechanical performance of both the tubing and the endplug joint of two-layer SiC
cladding is investigated under conditions associated with the LOCA. Specifically, SiC cladding mechanical
performance is investigated after exposure to 1,400˚C steam and after quenching from 1,200˚C into
either 100˚C or 90˚C atmospheric-pressure water. The samples consist of two-layer SiC, with an inner
SiC/SiC CMC layer and an outer monolith SiC layer. The relationship between mechanical performance
and sample architecture is investigated through ceramography and internal void characterization.

The two-layered SiC cladding design offered an as-received failure hoop stress of about 600 MPa, with
little strength reduction due to thermal shock, and the tube failure hoop stress remained above 200
MPa after 48 hour high-temperature steam oxidation. The cladding showed pseudo-ductile behavior
and failed in a non-frangible manner. The designs investigated for joint strength offered as-received
burst strength above 30 MPa, although the impact of thermal shock and oxidation showed possible
dependence on architecture. Overall, the cladding showed promising accident-tolerant performance.

Because the implementation of SiC is complicated by the need for an open gap and low plenum
pressure, thorium-based mixed oxides (MOX) are a promising fuel for SiC cladding because they have
higher thermal conductivity and lower fission gas release (FGR). Previous efforts at MIT have modified
the FRAPCON code to include thorium MOX fuel. In this work, the fission gas release and thermal
conductivity models of FRAPCON-3.4-MIT are validated against published data. The results of this
validation indicate a need to update the FGR model, which was accomplished in this work.

Thesis Supervisor: Michael P. Short, Ph.D.
Title: Assistant Professor of Nuclear Science and Engineering

Thesis Reader: Thomas J. McKrell, Ph.D.
Title: Research Scientist
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Acknowledgments
This work was supported under the United States Department of Energy award number DE-NE0000566
where MIT acted as a subcontractor to Westinghouse Electric. The samples investigated in this work
were manufactured and provided by General Atomics.

I would like to extend my gratitude to the late Professor Mujid Kazimi, who recruited me to this topic
and supervised my research until his death. He provided me with valuable direction, feedback, and
encouragement on my research. I also wish to express my gratitude to Professor Michael Short, who
assumed the role of my thesis supervisor upon Professor Kazimi’s death, and to Professor Jacopo
Buongiorno and Dr. Koroush Shirvan, who assumed leadership roles of the CANES group after Professor
Kazimi’s death and provided feedback and guidance on my research.

I would also like to thank Dr. Thomas McKrell, who provided invaluable guidance and support on the
experimental aspects of my research. His experience in experimentation immeasurably helped my
research and experimental skills, and his supervision and feedback during my frequent contact with the
project clients enhanced my communication skills. Furthermore, I appreciate Professor Ron Ballinger
and Peter Stahle for allowing me to use the load frame in the H. H. Uhlig corrosion laboratory. I also
recognize Dr. Christian Deck, Dr. George Jacobsen, and Dr. Hesham Khalifa of General Atomics and Dr.
Ed Lahoda and Dr. Peng Xu of Westinghouse Electric for providing feedback and suggestions for my
research. Their input helped direct the conduct of my research, and they provided feedback on the
results of my investigation.

I thank Pierre Guenoun with whom I worked closely and I also thank Yongsoo Park, whose concern for
lab safety went above-and-beyond expectations. Finally, I thank my family for their support and
assistance while I have been at MIT.

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Table of Contents
Abstract ......................................................................................................................................................... 3
Acknowledgments ......................................................................................................................................... 5
List of Figures .............................................................................................................................................. 10
List of Tables ............................................................................................................................................... 15
Nomenclature ............................................................................................................................................. 17
1. Introduction ........................................................................................................................................ 18
1.1. Motivation ................................................................................................................................... 18
1.2. Overview of Current LWR Cladding ............................................................................................ 19
1.2.1. LWR Cladding Overview ...................................................................................................... 19
1.2.2. Limitations of Current PWR Cladding ................................................................................. 19
1.3. Accident Tolerant Fuels............................................................................................................... 20
1.3.1. Motivation and Description of Accident Tolerant Fuels ..................................................... 20
1.3.2. Silicon Carbide for Nuclear Applications ............................................................................. 21
1.4. Objectives and Scope .................................................................................................................. 22
1.5. Thesis Organization ..................................................................................................................... 23
2. Performance Modeling of Thorium-Based Fuels ................................................................................ 25
2.1. Motivation ................................................................................................................................... 25
2.2. Fission Gas Release Mechanism.................................................................................................. 25
2.3. FRAPCON Fission Gas Release Model ......................................................................................... 26
2.3.1. Forsberg-Massih Model ...................................................................................................... 26
2.4. FRAPCON Modifications .............................................................................................................. 28
2.4.1. Thermal Conductivity Models ............................................................................................. 28
2.4.2. Fission Gas Release Models ................................................................................................ 34
2.5. Discussion .................................................................................................................................... 42
2.5.1. Densification Uncertainty ................................................................................................... 42
2.5.2. Comparison to Published Data ........................................................................................... 42
2.5.3. Implications for Fuel Performance ...................................................................................... 45
2.5.4. Implications for Silicon Carbide .......................................................................................... 46
3. Silicon Carbide Cladding ...................................................................................................................... 51
3.1. Uses of Silicon Carbide ................................................................................................................ 51
3.2. Previous Silicon Carbide LWR Cladding Research ....................................................................... 51
6
3.3. Manufacturing of Silicon Carbide Cladding ................................................................................. 53
3.3.1. Monolith SiC ........................................................................................................................ 53
3.3.2. SiC/SiC Composites ............................................................................................................. 53
3.3.3. Endplug ............................................................................................................................... 55
3.4. Silicon Carbide Cladding Options ................................................................................................ 56
4. Experimental Methodology ................................................................................................................ 59
4.1. Overview of Specimens ............................................................................................................... 59
4.1.1. Open-Ended Specimens ...................................................................................................... 61
4.1.2. Close-Ended Specimens ...................................................................................................... 61
4.2. Strength Test Facilities ................................................................................................................ 62
4.2.1. Pressurization Test Facility .................................................................................................. 63
4.2.2. Joint Strength Test Facility .................................................................................................. 70
4.3. Thermal Shock Facility ................................................................................................................ 73
4.4. Oxidation Facility......................................................................................................................... 74
5. XCT Analysis of Cladding Specimens ................................................................................................... 77
5.1. Motivation ................................................................................................................................... 77
5.2. Void Analysis Methodology ........................................................................................................ 77
5.2.1. Void Analysis Facility ........................................................................................................... 77
5.2.2. Image Processing ................................................................................................................ 77
5.3. Void Analysis of CMC .................................................................................................................. 81
5.3.1. CMC Void Data .................................................................................................................... 82
5.3.2. CMC Void Discussion ........................................................................................................... 87
5.3.3. CMC Void Implications ........................................................................................................ 89
5.4. Void Analysis of Endplug Joint .................................................................................................... 91
5.4.1. Endplug Joint Void Data ...................................................................................................... 91
5.4.2. Endplug Joint Void Discussion ............................................................................................. 93
5.4.3. Endplug Joint Void Implications .......................................................................................... 94
5.5. Conclusion ................................................................................................................................... 95
6. Experimental Results .......................................................................................................................... 97
6.1. Analysis of SiC Cladding Mechanical Performance As-Received................................................. 97
6.1.1. Motivation ........................................................................................................................... 97
6.1.2. Hoop Testing of As-Received Open-Ended Samples ........................................................... 97
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6.1.3. Joint Testing of As-Received Close-Ended Samples ............................................................ 98
6.1.4. Failure Observations ........................................................................................................... 99
6.2. Analysis of SiC Cladding Performance after Thermal-Shock ..................................................... 101
6.2.1. Motivation ......................................................................................................................... 101
6.2.2. Hoop Testing of Thermal-Shock Open-Ended Samples .................................................... 101
6.2.3. Joint Testing of Thermal-Shock Close-Ended Samples...................................................... 103
6.2.4. Failure Observations ......................................................................................................... 104
6.3. Analysis of SiC Cladding Performance after Steam Oxidation .................................................. 107
6.3.1. Motivation ......................................................................................................................... 107
6.3.2. Oxidation Data .................................................................................................................. 107
6.3.3. Hoop Testing Evaluation ................................................................................................... 109
6.3.4. Joint Testing Evaluation .................................................................................................... 111
6.3.5. Failure Observations ......................................................................................................... 113
6.4. Summary of Results .................................................................................................................. 116
6.4.1. As-Received Results .......................................................................................................... 116
6.4.2. Thermal-Shock Results ...................................................................................................... 116
6.4.3. High-Temperature Steam Oxidation Results .................................................................... 117
7. Discussion of Results ......................................................................................................................... 119
7.1. As-Received Discussion ............................................................................................................. 119
7.1.1. Hoop Test .......................................................................................................................... 119
7.1.2. Joint Test ........................................................................................................................... 121
7.1.3. Microstructural Analysis ................................................................................................... 122
7.2. Thermal-Shock Discussion ........................................................................................................ 125
7.2.1. Hoop Test .......................................................................................................................... 125
7.2.2. Joint Test ........................................................................................................................... 127
7.2.3. Microstructural Analysis ................................................................................................... 129
7.3. Oxidation Discussion ................................................................................................................. 132
7.3.1. Oxidation Microstructural Analysis ................................................................................... 132
7.3.2. Hoop Test .......................................................................................................................... 141
7.3.3. Joint Test ........................................................................................................................... 143
7.3.4. Microstructural Analysis ................................................................................................... 146
8. Conclusions and Recommendations for Future Work ...................................................................... 151
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8.1. Summary of Results .................................................................................................................. 151
8.2. Conclusions of As-Received Testing .......................................................................................... 152
8.3. Conclusions of Thermal-Shock Testing ..................................................................................... 154
8.4. Conclusions of High-Temperature Steam Oxidation Testing .................................................... 155
8.5. Recommendations for Future Work ......................................................................................... 156
Works Cited ............................................................................................................................................... 160

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List of Figures
Figure 1: Diffusivity for UO implemented in FRAPCON Massih model ...................................................... 28
2
Figure 2: Thermal conductivity comparison for urania............................................................................... 30
Figure 3: Urania thermal conductivity versus temperature comparison ................................................... 30
Figure 4: Comparison of FRAPCON urania thermal conductivity models ................................................... 31
Figure 5: Thermal conductivity comparison for thoria-urania .................................................................... 32
Figure 6: Thoria-urania thermal conductivity versus temperature comparison ........................................ 32
Figure 7: Thermal conductivity comparison for thoria-plutonia ................................................................ 33
Figure 8: Thoria-plutonia thermal conductivity versus temperature comparison ..................................... 34
Figure 9: Vicious cycle of fuel temperature increase .................................................................................. 36
Figure 10: FGR versus peak calculated historic thoria-urania fuel temperature ........................................ 37
Figure 11: Results of FGR modeling for thoria-urania rods ........................................................................ 37
Figure 12: Diffusivity for UO and modified thoria-urania model .............................................................. 38
2
Figure 13: Bruce-type 37-element bundle showing test rod locations (adapted from Karam (Karam, et al.,
2008)). ......................................................................................................................................................... 39
Figure 14: FGR versus calculated peak historic thoria-plutonia fuel temperature (#1 rods only) ............. 40
Figure 15: Results of FGR modeling for thoria-plutonia rods ..................................................................... 41
Figure 16: Diffusivity for UO and modified thoria-plutonia model ........................................................... 41
2
Figure 17: Comparison of modified FRAPCON thoria-urania diffusivity and published data (burnup
indicated) .................................................................................................................................................... 43
Figure 18: Comparison of FRACON UO diffusivity and published data (burnup indicated) ...................... 44
2
Figure 19: Comparison of calculated FGR LWBR fuel with and without thoria .......................................... 45
Figure 20: Comparison of calculated peak temperature for LWBR fuel with and without thoria.............. 45
Figure 21: Comparison of calculated FGR for AECL fuel with and without urania ..................................... 46
Figure 22: Comparison of calculated peak fuel temperature for AECL fuel with and without urania ....... 46
Figure 23: Comparison of fuel temperature for simulated rods ................................................................ 48
Figure 24: Comparison of FGR for simulated rods ...................................................................................... 48
Figure 25: Comparison of plenum pressure for simulated rods ................................................................. 49
Figure 26: Temperature comparison between diffusivity models.............................................................. 50
Figure 27: FGR comparison between diffusivity models ............................................................................ 50
Figure 28: EOL plenum pressure comparison between diffusivity models ................................................ 50
Figure 29: Schematic of TRISO fuel particle ................................................................................................ 52
Figure 30: Production of Hi-Nicalon fibers (Ishikawa, 1994) ...................................................................... 54
Figure 31: Comparison of failure behavior for monolith (left) and multilayer composite (right) tubing
(Carpenter, 2010) ........................................................................................................................................ 56
Figure 32: Cross-sectional SEM views of three-layer (left) and two-layer (right) samples ......................... 57
Figure 33: Graphic of sample architectural and geometric terminology .................................................... 60
Figure 34: Overview of the three architectures investigated ..................................................................... 60
Figure 35: Cross-sectional SEM view showing two-layer architecture ....................................................... 60
Figure 36: Typical GAOE sample and SEM close-up .................................................................................... 61
Figure 37: Typical GACE-A sample (left) and GACE-B sample (right) with SEM close-ups .......................... 62
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